In U.S. Pat. Nos. 4,169,090 and 4,208,323, the disclosures of which are incorporated herein by reference, both assigned to the assignee of this application, there are described procedures for isolating protein from protein source materials by contacting the protein source material with sodium chloride solution under critical pH and ionic strength conditions to solubilize the protein, and diluting the protein solution with water to a lower ionic strength to cause the formation of protein aggregates in the aqueous phase which settle and are collected as an amorphous protein micellar mass. The protein solution may be subjected to ultrafiltration prior to the dilution step and the settling may be enhanced by centrifugation.
When this procedure is applied to the isolation of protein from soybeans, the overall yield of isolate has been less than has been attained with other vegetable proteins. However, the soybean isolate is in a substantially undenatured form in contrast to soy isolates which are formed by the conventional isoelectric precipitation procedure, which are substantially denatured. The isoelectric precipitation procedure involves extracting the protein under highly alkaline pH conditions and acidifying the protein extract to the isoelectric point.